The present invention relates to a coated ion exchange substrate suitable for use in chromatography medium, and its method of forming.
In one form of liquid chromatography, columns are packed typically with discrete organic polymer granule or particle medium having functionally active surfaces. Preferable shapes for the discrete particle are spheres with regular surfaces. Materials for performing liquid chromatography are known where only thin outer surfaces of the chromatographic support materials are available for active exchange of ions with liquid media. For example, Small, et al. U.S. Pat. No. 4,101,460 describes an ion exchange composition comprising Component A, in insoluble synthetic resin substrate having ion-exchanging sites on its available surface, and Component B, a finely divided insoluble material, irreversibly attached thereto by electrostatic forces. Component B is typically deposited onto Component A from a latex.
A disadvantage regarding the latex coating procedure is that it can take a substantial period of time, e.g., days or even weeks, to make an optimized packed column. Such procedures typically require applying the coating after the column is packed which increases the manufacturing time and labor compared to synthetic methods which can provide a finished product prior to packing. This is because the packing can be made more efficiently in large batches rather than column-by-column. Also, latex synthesis is generally limited to water insoluble monomers which significantly limits choice in terms of available monomers.
Other particulate bed materials with ion exchange layering particles irreversibly bound to the outer surface of support particles are described in Barretto, U.S. Pat. No. 5,532,279. In one embodiment, Barretto describes forming a complex by contacting a suitable dispersant with monomer in an aqueous solution in which the monomer is insoluble. Under suitable conditions for suspension polymerization, the monomer will polymerize to form resin support particles having a dispersant irreversibly attached to those particles. Fine synthetic layering particles are bound to the support particles. A number of other different embodiments are disclosed for irreversible attachment.
Another form of chromatographic medium is made by forming a coating by binding a solution of a preformed polymer with saturated carbon chain backbones including leaving groups under hydrogen abstraction conditions to bind to preformed polymer to a substrate in the presence of a free-radical catalyst which removes leaving groups from the carbon chain to form the covalent bonds. See Srinivasan U.S. Pat. No. 6,074,541. This coating is disclosed for use with a variety of substrates including the inner wall of a conduit or particles for use in a packed bed.
Referring to anion analysis, there is a need for a hydroxide stable anion exchange phase capable of adequately separating bromate from chloride while still achieving good resolution of chlorate from bromate and nitrate. Bromate is of significant interest in water analysis in that it is consider to be a carcinogenic and is a potential byproduct of hypochlorite production often used to disinfect drinking water and ozonation also used to disinfect drinking water.